1. Field of the Invention
The present invention relates to a liquid jet head for ejecting a liquid from a nozzle to form images, characters, or a thin film material onto a recording medium. The present invention relates also to a liquid jet apparatus using the liquid jet head, and to a method of manufacturing a liquid jet head.
2. Description of the Related Art
In recent years, there has been used an ink-jet type liquid jet head for ejecting ink droplets on recording paper or the like to render characters or graphics thereon, or for ejecting a liquid material on a surface of an element substrate to form a functional thin film thereon. In such a liquid jet head, ink or a liquid material is supplied from a liquid tank via a supply tube to the liquid jet head, and ink or a liquid material filled into a channel is ejected from a nozzle which communicates with the channel. When ink is ejected, the liquid jet head or a recording medium on which a pattern of jetted liquid is to be recorded is moved to render a character or a graphics, or to form a functional thin film in a predetermined shape.
Japanese Patent No. 4658324 describes an ink jet head 100 in which ink channels which are a large number of grooves are formed in a sheet formed of a piezoelectric material. FIG. 16 is a sectional view of the ink jet head 100 illustrated in FIG. 1 of Japanese Patent No. 4658324. The ink jet head 100 has a three-layer structure of a cover 125, a PZT sheet 103 formed of a piezoelectric body, and a bottom cover 137. The cover 125 includes nozzles 127 for ejecting small droplets of ink. In an upper surface of the PZT sheet 103, there are formed ink channels 107 having a cross-section in a boat-like shape. The plurality of ink channels 107 are formed so as to be parallel to each other in a direction orthogonal to a longitudinal direction. Further, the ink channels adjacent to each other are defined by side walls 113. On an upper side-wall surface of each of the side walls 113, there is formed an electrode 115. Also on a side wall surface of the ink channels adjacent to each other, there is formed an electrode. Therefore, each of the side walls 113 is sandwiched between the electrodes (not shown) formed on the side wall surfaces of each of the ink channels adjacent to each other.
The ink channels 107 are communicated to the nozzles 127, respectively. In the PZT sheet 103, there are formed, on a bottom side, a supply duct 132 and a discharge duct 133. The supply duct 132 and the discharge duct 133 are communicated to the ink channel 107 in vicinities of both end portions thereof. The ink is supplied through the supply duct 132, and the ink is discharged through the discharge duct 133. In a surface of the PZT sheet 103 at a right end portion and a left end portion of the ink channel 107, there are formed concave portions 129, respectively. On a bottom surface of each of the concave portions 129, there is formed an electrode (not shown), which is electrically conducted to the electrode 115 formed on the side wall surface of each of the ink channels 107. A connection terminal 134 is received in the concave portion 129. The connection terminal 134 is electrically connected to the electrode formed on the bottom surface of the concave portion 129.
Operation of the ink jet head 100 is as follows. When a drive signal is applied from the connection terminal 134, the drive signal is applied to the electrodes 115 which sandwich the side wail 113. Then, the side wall 113 undergoes thickness shear deformation to change the capacity of the ink channel 107. This causes pressure fluctuations of ink filled into the ink channel 107 to eject an ink droplet through the nozzle 127. This kind of an ink jet head is called a side shoot type and through flow type ink jet head. Ink in the ink channel 107 is supplied from the supply duct 132 and is discharged from the discharge duct 133 to be circulated. Therefore, even if air bubbles enter the ink channel, such air bubbles may be discharged in a short time, and maintenance may be performed without using a cap structure and without using a service station.
Japanese Patent No. 4263742 describes an ink jet head having the structure different from that of the above-mentioned inkjet head. FIG. 17 is a partial perspective view of the ink jet head described in Japanese Patent No. 4263742. The ink jet head includes two antechambers 931 and 941 on a lower side which are separated from each other by a partition, two plenum chambers 980′ and 980″ on an upper side which are separated from the lower side by a base plate 900, trapezoidal PZT blocks 110 which separate the two plenum chambers 980′ and 980″ from each other and which are formed of a piezoelectric body, and a plate 991 which closes upper portions of the PZT blocks 110 and which has a plurality of nozzles 994 formed therein. An inlet manifold 930 is placed in the antechamber 931. The inlet manifold 930 may supply ink to the plenum chamber 980′ via ports 972 formed in the base plate 900. An outlet manifold 940 is placed in the antechamber 941 and discharges ink via ports formed in the base plate 900. Ink which flows into the plenum chamber 980′ flows via spaces between the trapezoidal PZT blocks 110 to the plenum chamber 980″.
A drive electrode is formed on each side surface of each of the PZT blocks 110. Two extracting electrodes which are connected to the drive electrodes and which are electrically separated from each other are formed on an upper surface and an inclined surface of each of the PZT blocks 110 (see FIG. 7 of Japanese Patent No. 4658324). A large number of conductive tracks are formed on an upper surface of the base plate 900 to be electrically connected to the above-mentioned extracting electrodes (see FIGS. 14 and 15 of Japanese Patent No. 4658324). By applying a drive signal via the conductive tracks and the extracting electrodes to the drive electrodes, the PZT blocks 110 undergo shear deformation and a pressure wave is produced in ink filled into a chamber between the PZT blocks 110 to eject ink through the corresponding nozzle 994.
In recent years, downsizing of an ink jet head is required. However, downsizing of the ink jet head described in Japanese Patent No. 4658324 has a ceiling. In the ink jet head 100 of Japanese Patent No. 4658324, the ink channel 107 is in the shape of a boat which is convex on a bottom side. This is because a disc-like dicing blade (also referred to as a diamond wheel) is used when grooves as the ink channels 107 are formed in the front surface of the PZT sheet 103, and the shape of the ends of the grooves reflects the outside shape of the dicing blade. For example, when a dicing blade having a diameter of 4 inches is used to form the ink channels 107 having a depth of 350 μm, the length on the PZT sheet 103 to which the circular shape of the dicing blade is transferred is about 12 mm in total. This means that, when the ink channels 107 are formed, in addition to the channel length of the ink channels 107, dead spaces having an arc-shaped bottom and having lengths of about 12 mm in total need to be secured at both ends thereof. Even if a dicing blade having a diameter of 2 inches is used, dead spaces having lengths of about 8.3 mm in total are necessary at both ends of the ink channels 107. Therefore, the ink jet head 100 cannot be downsized, and in addition, the number of the PZT sheets 103 obtained by dividing a PZT substrate is small, which increases the cost.
The ink jet head described in Japanese Patent No. 4263742 is formed by laminating on the base plate 900 the PZT blocks 110 which form the ink channels. Therefore, it is not necessary to secure dead spaces for forming the ink channels as in the ink jet head described in Japanese Patent No. 4658324. However, in the ink jet head described in Japanese Patent No. 4263742, it is necessary to form a large number of conductive tracks which are electrically separated from one another on the upper surfaces and the inclined surfaces of the PZT blocks 110 and on the upper surface of the base plate 900, and the patterning of the electrodes is complicated and processing takes a long time.
More specifically, there is a height difference of, for example, about 300 μm or more between the upper surfaces of the trapezoidal PZT blocks 110 and the upper surface of the base plate 900. Therefore, it is difficult to collectively pattern a conductive layer deposited on the surfaces thereof by photolithography or etching and to separate the individual electrodes. Therefore, the electrodes are patterned by a method in which a laser is applied to the conductive layer deposited on the upper surfaces and the inclined surfaces of the PZT blocks 110 to locally vaporize the conductor to be removed. However, the number of the electrodes to be formed is several hundreds or more, and thus, it takes a very long time to pattern the electrodes.
Further, in Japanese Patent No. 4658324, the shape of both ends of the ink channels 107 reflects the outside shape of the dicing blade and a stagnation region, in which the flow of ink stagnates, is formed between the ink channels 107 and the supply duct 132 or the discharge duct 133 formed thereunder. Similarly, in the antechamber 931 of the ink jet head of Japanese Patent No. 4263742, ink which flows from the inlet manifold 930 flows to the ports 972, but the inlet manifold 930 is formed of a porous material, and thus, ink fills the antechamber 931. Therefore, a stagnation region, in which the flow of ink stagnates, is formed in a corner of a bottom surface or an upper surface of the antechamber 931, and air bubbles or foreign matter which enters ink remains in the flow path, which is a cause of ejection failure of the nozzles 994.